The Largest Structure Ever Observed in the Universe

By Rebecca J. Rosen

At 4 *billion* light years across, this quote-unquote "object" throws astronomical assumptions that go back to Einstein into doubt.

A computer visualization of quasar cluster U1.27 or, more colloquially, Huge-LQG, the largest object ever identified in the universe (Roger G. Clowes)

Those dots may not look like much, but they represent the 73 quasars that in all make up the largest object ever discovered in our observable universe. At its longest, the quasar group (known technically as U1.27 but more colloquially as Huge-LQG for "large quasar group") runs about 4 *billion* light years, and about 1.6 billion at most points. For comparison, our Milky Way galaxy is approximately just ("just") 100,000 light years across.

Each of the 73 quasars is (or was, as the light has traveled billions of years to reach our telescopes) the center of a galaxy in the early universe. The group was discovered by a team led by Roger G. Clowes at the University of Central Lancashire in the data provided by the Sloan Digital Sky Survey and published in Monthly Notices of the Royal Astronomical Society on Friday.

The Huge-LQG is located very near to another quasar cluster, discovered by Clowes in 1991, known as Clowes & Campusano LQG (CCLQG). Because the Huge-LQG is so, well, huge, and particularly because it is located so near another huge object, the results throw into doubt the cosmological principle, an assumption that traces back to Einstein, which presupposed that given a large enough scale, the universe should look the same everywhere you look. But with an object this extraordinarily large, it seems that that region of the universe is quite unusual. Even given the cosmological principle, you expect to see some unusually large features, but the Huge-LQG exceeds even the largest expected size "substantially," Clowes wrote to me over email. "Some of our previous findings came close, but didn't exceed it. This one does."

Clowes wrote to me over email, explaining that the cosmological principle has "seemed plausible, but it's never really been demonstrated beyond reasonable doubt." Over time we have tried to tinker with the homogeneity scale of the cosmological principle to accommodate for unusually large objects. "But," Clowes writes, "this is a few percent of the size of the observable universe, so we might not be able to do that kind of thing any more."